1. Field of the Invention
The present invention is directed to collector assemblies used for collecting spent electrons in linear beam electron devices. More particularly, the invention is directed to a collector assembly having a hot-inserted molybdenum sleeve to separate the ceramic collector core from a corresponding heat sink in order to provide improved high temperature operation.
2. Description of Related Art
Linear beam electron devices are well known in the art for generating and amplifying high frequency signals. In a linear beam device, an electron gun comprising a cathode and an anode generates a linear beam of electrons. The electron beam passes through an interaction structure, or drift tube, in which the energy of the beam is transferred to an electromagnetic signal. At the end of the drift tube, the spent electrons of the beam pass into a collector structure that captures the electrons and recovers a portion of their remaining energy. Electrodes disposed within the collector structure are used to collect the spent electrons at close to their remaining energy level in order to return the electrons to the power source of the linear beam electron device. Energy of the spent electrons that cannot be collected onto the electrodes is dissipated into the collector structure in the form of heat.
Since linear beam electron devices operate at very high power levels, the collector structure must be capable of withstanding very high operating temperatures, e.g., above 200.degree. Celsius. Moreover, the collector structure must stand off the voltage potential between individual ones of the collector electrodes. In view of these demanding operational requirements, the central core of the collector structure is often comprised of a thermally rugged and electrically non-conductive material, such as ceramic. To remove the heat from the collector core, collector assemblies generally also include a heat sink provided in contact with the outer surface of the collector core. Typically, the heat sink is made of a material having good thermal conductivity, such as copper or aluminum.
A drawback of such prior art collector assemblies is that the ceramic collector core and metal heat sink can be incompatible due to the differences in their respective rates of thermal expansion. In one method of manufacture known in the art, the ceramic collector is dimensioned to fit into a corresponding opening in the heat sink at room temperature. During high temperature operation, the metal heat sink expands at a higher rate than the ceramic core, causing the heat sink to expand away from the collector core and leave a gap between the two adjacent structures. The heat sink is thereby no longer effective in removing heat from within the ceramic collector core, resulting in excessive stress of the collector core and ultimately failure of the component. A proposed solution to this problem is to dimension the ceramic collector core to fit the thermally expanded size of the heat sink, and to insert the collector core into the heat sink with the heat sink pre-heated to the operational temperature. This method is not practical due to the difficulty of constructing the entire collector assembly in a high temperature environment.
It would therefore be highly desirable to provide a collector structure having a ceramic collector core that permits high temperature operation without the drawbacks of the prior art. More particularly, it would be desirable to provide a collector assembly having efficient heat transfer from the ceramic collector core to the surrounding heat sink while operating at relatively high temperatures.